This invention relates to a flexible stamp apparatus for printing three dimensional spherical and/or curved objects.
It is presently known to use a hollow, half silicon spherical shape for printing spherical objects, such as toy balls. This silicon shape has a thickness of about 2 cm and it is mounted on a hollow flexible stamp or pad holder. The silicon shape and the pad holder are designated hereafter as the xe2x80x9cthe padxe2x80x9d.
The pad holder is made of an undeformable material and has the shape of a drum. It forms together with the silicon shape, an hermetically closed space having only one aperture as contact with the outside. At this sole aperture, a flexible tube having a sufficiently great diameter is connected to a pressure vessel. Said pressure vessel is not represented at scale. This pressure vessel needs to have a volume which can contain 10 to 100 times the volume of the pad indeed. The pressure vessel is yet generally kept under a light over-pressure by means of a separate pressure regulator.
This construction serves for keeping the pressure in the pad as constant as possible during the printing cycle. Indeed, a pressure variation in the pad results in the dilatation or the retraction of the silicon part. Owing to this, the image on the silicon part becomes bigger or smaller with a bad printing quality on the printed spherical objects. The different times of the printing cycle of the prior art show subsequently a rest position wherein the pressure in the pad is equal to the one in the pressure vessel. This pressure is designated hereafter with the reference P.
The pad is moved from the rest position to said object to be printed in a relative movement according to arrow F and it bends over the object to be printed. The air in the pad is pressed to the pressure vessel through the flexible tube. However, despite the fact that the volume of the pressure vessel is several times greater than the content of the pad, this displacement of air volumes yet results in a slight increase of the pressure in the pad and vessel, which is designated hereafter by the reference Pxe2x80x2.
After this, the pad returns to its original state according to the direction of arrow F, i.e. to the rest position. The air now moves back from the pressure vessel to the pad. The pressure in the system now becomes greater than P, which is referred to hereafter with Pxe2x80x3, but during this part of the cycle, the latter decreases again so as to become pressure P again.
This above-mentioned known system is a closed circuit wherein the air, which is pressed out of the pad during the printing and inking stage, goes back to the pressure vessel. When the pad goes back to its original position, the air returns to the pad again from the pressure vessel.
The great advantage of this system consists in that despite the fact that the volume of the pressure vessel is several times greater than the volume of the pad, there is still a small pressure variation, i.e. P, Pxe2x80x2, Pxe2x80x3, which affects unfavourably the printing quality during the pad action on the objects to be printed.
This invention aims at remediating the above-mentioned drawback. Thus in this invention, a hollow pad as above is used, wherein instead of using a closed circuit, the pad is now incorporated in an open circuit according to the invention.
Not withstanding that the apparatus according to the invention has a lower air consumption, it yet enables determining the pressure in the pad in a very accurate way at each time of the printing cycle. This is a very important parameter for printing at least partially spherical objects, particularly in connection with the printing quality thereof, the importance whereof increases as nowadays the requirements set for the printing quality are always becoming stronger.
Further properties and particularities are defined in the appended claims.
Some exemplary embodiments of the system according to the invention are described hereafter in the light of the appended drawings.
This invention also relates to a process for printing at least partially spherical and/or curved three dimensional objects. It is to be understood that a substantially differentiating element in this invention consists in that an open loop is used here and not a closed loop, wherein in addition the inlet side and the outlet of the pad are clearly separated from each other. Thanks to this specific process according to the invention a remarkably higher printing quality is achieved.